I just looked at the differences and it looks like the D6 is a thinner version of the D4 so I think i made the right decision of goin with the D4 for now.
If i have issues then maybe I'll try the D6 later.
The best thing about changing the fluid in the manual is that it's really so easy and inexpensive.
20 bucks for fluid and can be done in about 30 minutes in the front of my house.